Electrodeposition of tin or lead-tin alloys



Patented Nov. 29, 1949 UNITED STATES PATENT OFFICE ELECTRODEPOSITION F TIN OR LEAD-TIN ALLOYS- Erank L. Clifton, Detroit, Mich., assignor to. General Motors Corporation, Detroit, Mich., a corporation of Delaware 9 Claims.

The invention relatesto theelectrodenosition of tin or alloys of tin and particularly alloys consisting principally of lead and, tin.

Lead-tin alloys are useful in various industrial 2% ates. If a bath so made is electrolyzed, preferably with anodes containing both tin and lead, an alloy of the two metals is deposited. With the use of anodes of 10% tin and 90% lead,

fields, for example, as coatings. to protect base 5 for example, the content of tin in the deposit, metals against corrosion, and as bearings, or parts which may be low at first, will increase until it thereof. The presence of a small proportion of reaches approximately the same proportion as tin in lead prevents the lead from being attacked that present in the anodes. and dissolved by corrosive acids that are pro- As another example of a method of making up duced in lubricating oils, especially at high tema bath for plating a lead-tin alloy, I have used peraturesy.itis comm n P e to a lead plating bath constituted in accordance employ such alloys as. hearing babbitts or for with the above mentioned patent, and passed bearin surfaces. through it current at about forty amperes per It is Well known that alloys of lead and tin square foot, with tin anodes, for about sixty can be deposited electrolytically, and baths in hours at room temperature. At this. time a do.- which the metalsv are presentin the form of posit was obtained containing approximately fiuoborates have been used, for that. purpose. 15% of tin. Upon restoring the original lead Such baths, however, are inconvenient for several content of the bath, by addition of one-half reasons and are difiicult to control. I have found pound per gallon of lead sulfamate. plating salts, that baths in which the metals are. present. as the deposit then obtained, when analyzed, showed compounds of sulfamic acid provide.- a. more the alloy to be approximately 10% tin and 90% satisfactory operation and better deposit. lead. The initial tin content of the bath can, of

Sulfamate baths for deposition of lead alone course, be made less or greater by correspond:- are known and are disclosed, for example, in ingly decreasing or increasing the time of elec- Patent 2,318,592, Cuperty, May 11, 1943. In 9.0- '25 trolysis. If any sludge appears, the bath may cordance with the present invention, I use a sulbe filtered. It will also be understood that the famate bath containing tin to which, if it be deconditions given above are by way of illustrasired to deposit a lead-tin alloy, a suitable quantion merely, and may be widely varied. tity of lead sulfamate may be added to form a In operating the baths for plating, I find that bath from which both lead and tin may be 3 the temperature should not exceed 115 F., and readily deposited. should preferably be about room temperature, As an illustration of one method of making up cooling coils being used if necessary. Such coils, a tin sulfamate bath, I have formed the tin salt and the tanks also, should, of course, be proby electrolytic action in a bath containing sultected against action of the acid as by rubber or famic acid and tin anodes. For example, asoluglass coatings or other commercial acid-resistant tion of 50 gr. sulfamic acid in 1 liter of water material. The pH of the bath may be regulated may be provided. Upon placing in such solution by additions of sulfamic acid to approximately a tin anode and copper cathode and passing 1.4-2.4. therethrough current at approximately 12 am- In planting the lead-tin alloy, the current peres per sq. ft. of cathode area, operating at 40 density is an important factor, especially as the room temperature, a visible deposit of tin will be percentage of tin in the deposit increases with obtained almost immediately. After electrolysis increase in current density. With the bath confor several hours, analysis of the bath will show stituted as above set forth, the tin content of the the presence of tin to the amount of upwards of 5 deposit can be varied from between 5% and 10% gr. per liter. at 20 amps. per sq. ft. to as high as 30% at 90 to Tin may be deposited from such a bath even 100 amps. It is therefore desirable, in order to though a carbon anode be substituted for the tin obtain a fairly uniform composition of alloy on anode. The use of tin anodes is, however, prefdifferent plated areas, so to arrange the anodes erable in order to maintain the tin content. that a correspondingly uniform current density is If it be desired to make up a bath from which secured. In general, a current density of 10-30 both lead and tin can be deposited simultaneousamps. per sq. ft. of cathode area is recommended, 1y, a tin bath constituted as above may have although, with agitation, as high as '75 amperes added thereto lead sulfamate or a salt of lead may be satisfactorily employed and higher temwhich will dissolve in the bath with the formaperatures than are desirable in a still bath. Suittion of the sulfamate, for example, lead carbonable agitation may be effected by cathode movement at about 6-20 ft. per minute. By suitable regulation of bath content and current density, I have obtained deposits as desired, ranging from approximately 1% to as high as 30% tin, with variations in different areas of not more than about 1-2%. Thorough cleaning of the base metal is required in order to secure good adhesion of the deposit.

As above pointed out, I prefer to maintain the metal content of the bath by solution of suitable anodes. In the case of the lead-tin bath, these anodes should be of the same composition as that desired in the deposit. Since anodes containin lead and/or tin readily dissolve during electrolysis, I have not found it necessary to add salts to maintain the metal content of the baths.

I claim:

1. The process of producing an electrolytic bath for deposition of tin consisting essentially in providing an aqueous solution of sulfamic acid, electrolyzing said solution with an anode of tin and forming thereby in said solution a compound of tin with sulfamic acid.

2. The process of preparing an electrolytic bath for simultaneous deposition of tin and lead consisting essentially in providing an aqueous solution of sulfamic acid, placing in said solution an anode of tin, electrolyzing said solution, thereby forming therein a compound of tin with sulfamic acid soluble in said solution adding to the solution lead sulfamate, and adjusting the sulfamic acid content to result in a pH of approximately 1.4 to 2.4.

3. The process of preparing an electrolytic bath for simultaneous deposition of lead and tin consisting essentially in providing an aqueous solution of sulfamic acid and lead sulfamate, electrolyzing said solution with the use of a tin anode until a lead-tin deposit is obtained in which the tin content is between 1% and 30%, then adding to the bath a compound of lead capable of restoring the lead lost by electrodeposition.

4. An electrolytic bath from Which tin may be electrodeposited consisting essentially of an aqueous solution of sulfamic acid and a compound of tin formed by reaction between tin and sulfamic acid by electrolysis of a tin anode in an aqueous sulfamic acid solution, said compound being readily soluble in such solution.

5. A bath for electrodeposition of an alloy of lead and tin, said bath consisting essentially of an aqueous solution of sulfamic acid, lead sulfamate, and the product of reaction between tin and sulfamic acid produced by electrolyzing a tin anode in an aqueous solution of sulfamic acid.

, 6. A bath for electrodeposition of an alloy of lead and tin consisting essentially of an aqueous solution of sulfamic acid, lead sulfamate and the product of electrolyzing a tin anode in an aqueous sulfamic acid solution, said product and the lead salt being present in quantities sufficient to yield, upon electrolyzing a deposit of lead-tin alloy having 1% to 30% tin.

' 7. The process of electrodepositing an alloy of lead and tin by electrolyzing an aqueous solution having as its essential ingredients water, sulfamic acid, lead sulfamate and a compound of tin and sulfamic acid, the lead and tin salts being present in proportions to yield a deposit having a tin content of 1% to 30%,

8. The process as set forth in claim '7 including maintaining the content of tin and lead in the solution by use of anodes having approximately the content of the alloy to be deposited.

9. The process as set forth in claim '7 including maintaining the solution at a pH of approximately 1.4 to 2.4 by adjustment of the sulfamic acid content.

FRANK L. CLIFTON.

REFERENCES CITED The following references are of record in the file of this patent:

Chemical Abstracts, vol. 34. (1940') pp. 677, 678.

Transactions of the Electrochemical Society, vol.40 (1921), p. 291.

Chemica E Industria (Italy), 21, pp. 478-491 (1939). 

